What's the role of documentation in QA?

Sometimes, for people who are new to the software line (and specifically new to the testing business), there are questions about how important documentation would be to regular Quality work. After all, the major work is about testing some software and getting the bugs resolved, how important could testing be ? Well, the role of documentation in enabling the success of QA activities is critical. Note that documentation can be in electronic form as well, no necessity that it should be only paper, and in fact, recent trends are more towards having electronic forms that can be placed in source control areas in their specific directory locations.
QA practices should be documented such that they are repeatable, and are not dependent on individual people. Software artifacts and processes such as requirement and design specifications, design documents such as architecture, HLD, LLD, business rules, inspection reports, configuration control design and operational documents, code changes, software test plans, test cases, bug reports and decision making on important bugs, user manuals, etc. should all be documented such that these can be referred later (and prove very useful in case the project personnel are changed or should be transitioned to other teams).
As a part of documentation, there needs to be a system for easily finding and obtaining documents and determining what documentation will have a particular piece of information. Change management for documentation should be used in all cases, else you will find later that it is hard to figure out why something changed and what were the reasons behind it.
One of the most common reasons for failures or overruns / delays in a complex software project is to have poorly documented requirements specifications. Requirement specifications are the details describing an application's externally-perceived functionality and properties. The condition for requirements should be clear, complete, reasonably detailed, cohesive, attainable, and testable. A non-testable requirement would be, for example, 'user-friendly' (too subjective). A testable requirement would be something like 'user needs to enter their date of birth while creating their profile'. Determining and organizing requirements details in a useful and efficient way can be a difficult effort; different methods are available depending on the particular project.
Care should be taken to involve ALL of a project's significant 'customers' and important stakeholders in the requirements process. 'Customers' could be in-house personnel or out, and could include end-users, customer acceptance testers, customer contract officers, customer management, future software maintenance engineers, salespeople, etc. Anyone who could later derail the project if their expectations aren't met should be included if possible. This also helps in ensuring that changes later are minimized (can never be eliminated).
Organizations vary considerably in their handling of requirements specifications. Ideally, the requirements are spelled out in a document with statements such as 'The product shall.....'. 'Design' specifications should not be confused with 'requirements'; design specifications should be traceable back to the requirements.
In some organizations requirements may end up in high level project plans, functional specification documents, in design documents, or in other documents at various levels of detail. No matter what they are called, some type of documentation with detailed requirements will be needed by testers in order to properly plan and execute tests. Without such documentation, there will be no clear-cut way to determine if a software application is performing correctly.
Test plans need to be documented properly with good change control, since a test plan forms the basis of determining the areas of testing, scope, responsibilities, etc. A test plan forms the first level of generation of confidence in the test strategy for the project.